The present invention relates to a method for corrosion-proofing of a water system of the type specified in the introduction to the claim.
Soluble anodes are used in prior art systems for electrolytic water treatment. Such anodes in controlled quantities depending on water consumption form anodic material salts which are passed to the following pipe system with the effect that if e.g. aluminium is used, a cathodic inhibitor is formed which has a tendency to precipitation on the metal surfaces.
If the same method is used, a potential-determined contact is obtained at the prior art electrolyses between the anions of the water and the positively charged aluminium cation formed at the anode with salt formation thereon which often has a tendency to precipitation so that flocculation can be made with the result that the total salt content in the water is reduced. This type of system is used primarily for industrial plants and especially for process water.
The use of prior art technology creates a problem if the water content of active anions is high as the production of anodic aluminium ions has to be related to the anion content in the water if a surplus of active aluminium hydroxide is required which is to prevent corrosion in a pipe system. It has, therefore, been experienced that dissolution of the anodic aluminium is to be controlled by the parameters of the water; not just the above-mentioned cations, but also the water temperature which affects the reaction tendency between the ions. There are prior art examples that the amperage--and thus the solution contingent on Faraday--is to be increased by factor 10 in order that every liter of treated water can have a required aluminium hydroxide content in order that the corrosion-proofing effect can be obtained at a temperature difference of approx. 50.degree. C. which is normal between cold and hot tap water. This factor implies that the treatment of hot water creates a considerable formation of sludge which it must be possible to remove expediently from the water. The effect is that the construction of the water installation has to pay special attention hereto as it is not desirable that sludge should pass to the pipe system. For the same reason, electrolytic water treatment normally requires a minimum water treatment time of 20 minutes which has proved adequate to secure flocculation and sedimentation.
If the water is also calcareous, the increased current as mentioned above also has the effect that a strong pH-conditional precipitation requiring regular cleaning will occur on the cathode surfaces of the plant. Besides, the content of anions in the water will have a tendency to passivate the relatively large surface of the aluminium anode. Especially phosphate and silicate may give trouble.